Data / Rankings / Median Air Quality Index (US EPA) / Counties in Wisconsin

Counties in Wisconsin by median Air Quality Index (US EPA)

Grant County had the highest median Air Quality Index (US EPA) of 35 counties in 2003, at 52. Forest County had the lowest, at 8. The median was 44. Source: the U.S. Environmental Protection Agency.

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Highest52Grant County
Lowest8Forest County
Median4435 counties

Map of counties, 2003

Ashland County: 29 indexBrown County: 44 indexColumbia County: 47 indexDane County: 49 indexDodge County: 49 indexDoor County: 44 indexDouglas County: 20 indexEau Claire County: 14 indexFlorence County: 41 indexFond du Lac County: 44 indexForest County: 8 indexGrant County: 52 indexGreen County: 46 indexJefferson County: 46 indexKenosha County: 47 indexKewaunee County: 44 indexManitowoc County: 45 indexMarathon County: 44 indexMilwaukee County: 42 indexOneida County: 42 indexOutagamie County: 44 indexOzaukee County: 46 indexRacine County: 38 indexRock County: 47 indexSt. Croix County: 44 indexSauk County: 37 indexSheboygan County: 44 indexTaylor County: 39 indexVernon County: 46 indexVilas County: 40 indexWalworth County: 46 indexWashington County: 44 indexWaukesha County: 50 indexWinnebago County: 45 indexWood County: 52 index
  • Under 39
  • 39 to 44
  • 44 to 46
  • 46 to 47
  • 47 and over
  • No data
index, 2003. Hatched areas have no value for this period. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Boundaries: U.S. Census Bureau cartographic boundary files.

All counties, 2003

Grant County: 52 indexGrant County52Wood County: 52 indexWood County52Waukesha County: 50 indexWaukesha County50Dane County: 49 indexDane County49Dodge County: 49 indexDodge County49Columbia County: 47 indexColumbia County47Kenosha County: 47 indexKenosha County47Rock County: 47 indexRock County47Green County: 46 indexGreen County46Jefferson County: 46 indexJefferson County46Ozaukee County: 46 indexOzaukee County46Vernon County: 46 indexVernon County46Walworth County: 46 indexWalworth County46Manitowoc County: 45 indexManitowoc County45Winnebago County: 45 indexWinnebago County45Brown County: 44 indexBrown County44Door County: 44 indexDoor County44Fond du Lac County: 44 indexFond du Lac County44Kewaunee County: 44 indexKewaunee County44Marathon County: 44 indexMarathon County44Outagamie County: 44 indexOutagamie County44Sheboygan County: 44 indexSheboygan County44St. Croix County: 44 indexSt. Croix County44Washington County: 44 indexWashington County44Milwaukee County: 42 indexMilwaukee County42Oneida County: 42 indexOneida County42Florence County: 41 indexFlorence County41Vilas County: 40 indexVilas County40Taylor County: 39 indexTaylor County39Racine County: 38 indexRacine County38Sauk County: 37 indexSauk County37Ashland County: 29 indexAshland County29Douglas County: 20 indexDouglas County20Eau Claire County: 14 indexEau Claire County14Forest County: 8 indexForest County8Grant County: 52 indexGrant County52Wood County: 52 indexWood County52Waukesha County: 50 indexWaukesha County50Dane County: 49 indexDane County49Dodge County: 49 indexDodge County49Columbia County: 47 indexColumbia County47Kenosha County: 47 indexKenosha County47Rock County: 47 indexRock County47Green County: 46 indexGreen County46Jefferson County: 46 indexJefferson County46Ozaukee County: 46 indexOzaukee County46Vernon County: 46 indexVernon County46Walworth County: 46 indexWalworth County46Manitowoc County: 45 indexManitowoc County45Winnebago County: 45 indexWinnebago County45Brown County: 44 indexBrown County44Door County: 44 indexDoor County44Fond du Lac County: 44 indexFond du Lac County44Kewaunee County: 44 indexKewaunee County44Marathon County: 44 indexMarathon County44Outagamie County: 44 indexOutagamie County44Sheboygan County: 44 indexSheboygan County44St. Croix County: 44 indexSt. Croix County44Washington County: 44 indexWashington County44Milwaukee County: 42 indexMilwaukee County42Oneida County: 42 indexOneida County42Florence County: 41 indexFlorence County41Vilas County: 40 indexVilas County40Taylor County: 39 indexTaylor County39Racine County: 38 indexRacine County38Sauk County: 37 indexSauk County37Ashland County: 29 indexAshland County29Douglas County: 20 indexDouglas County20Eau Claire County: 14 indexEau Claire County14Forest County: 8 indexForest County8
index. Source: EPA, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12.

Full ranking

RankCounties2003
index		Change on 2002
1Grant County520
1Wood County52+1
3Waukesha County50-3
4Dane County49+1
4Dodge County49+6
6Columbia County47+3
6Kenosha County47-1
6Rock County47-1
9Green County46+2
9Jefferson County46-2
9Ozaukee County46+1
9Vernon County46+3
9Walworth County460
14Manitowoc County45+2
14Winnebago County45+1
16Brown County44+1
16Door County44+3
16Fond du Lac County44+1
16Kewaunee County44+2
16Marathon County44+2
16Outagamie County44+2
16Sheboygan County440
16St. Croix County44+2
16Washington County440
25Milwaukee County42-7
25Oneida County42+5
27Florence County41+3
28Vilas County40+8
29Taylor County39+3
30Racine County38+17
31Sauk County370
32Ashland County29+12
33Douglas County20-18
34Eau Claire County14+1
35Forest County8-2

Other periods

About this ranking

Median of the daily Air Quality Index (AQI) values of a US county over the days of the year with an AQI, from the EPA AirData annual summaries.

More on how it is measured
  • The daily county AQI is the highest AQI among the monitors and pollutants reported that day (ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide).
  • Lower is cleaner: 0 to 50 is good, 51 to 100 moderate and above 100 unhealthy for sensitive groups.

United States counties with air quality monitors only, about 1,000 of some 3,100 in recent years; a county without monitors has no value. The number of days with an AQI differs between counties because some monitors run only in the ozone season.

Every value in the ranking comes from the same publisher and the same period, so the counties are compared on one definition. 13 counties with data in other periods have no value for 2003 and are left out rather than filled from another source. Equal values share a rank.

How to cite

U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.

Citation styles

The publisher is the author. Invokely is named only as the place the figures were read, where a style asks for it.

APA 7

U.S. Environmental Protection Agency. (2026). EPA AirData annual AQI by county: median daily AQI (Counties in Wisconsin by median Air Quality Index (US EPA), 2003) [Data set]. Retrieved October 12, 2026, from https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual

MLA 9

EPA AirData annual AQI by county: median daily AQI, Counties in Wisconsin by median Air Quality Index (US EPA), 2003. U.S. Environmental Protection Agency, 13 July 2026, https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Invokely, https://invokely.ai/rankings/median-air-quality-index/wisconsin-counties?period=2003. Accessed 12 Oct. 2026.

Chicago (author-date)

U.S. Environmental Protection Agency. 2026. EPA AirData annual AQI by county: median daily AQI. Counties in Wisconsin by median Air Quality Index (US EPA), 2003. Dataset. Accessed October 12, 2026. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Also distributed by Invokely, https://invokely.ai/rankings/median-air-quality-index/wisconsin-counties?period=2003.

Harvard

U.S. Environmental Protection Agency (2026) EPA AirData annual AQI by county: median daily AQI, Counties in Wisconsin by median Air Quality Index (US EPA), 2003 [Dataset]. Available at: https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual, via Invokely: https://invokely.ai/rankings/median-air-quality-index/wisconsin-counties?period=2003 (Accessed: 12 October 2026).

BibTeX
@misc{environmental_counties_in_wisconsin_by_2003,
  author = {{U.S. Environmental Protection Agency}},
  title = {{EPA AirData annual AQI by county: median daily AQI: Counties in Wisconsin by median Air Quality Index (US EPA), 2003}},
  year = {2026},
  howpublished = {Data set},
  url = {https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual},
  urldate = {2026-10-12},
  note = {Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/wisconsin-counties?period=2003. Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download\_files.html\#Annual. Retrieved 2026-10-12.},
}
RIS
TY  - DATA
AU  - U.S. Environmental Protection Agency
TI  - EPA AirData annual AQI by county: median daily AQI: Counties in Wisconsin by median Air Quality Index (US EPA), 2003
PY  - 2026
DA  - 2026/07/13
PB  - U.S. Environmental Protection Agency
DB  - Invokely
UR  - https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual
L2  - https://invokely.ai/rankings/median-air-quality-index/wisconsin-counties?period=2003
Y2  - 2026/10/12
N1  - Accessed via Invokely, https://invokely.ai/rankings/median-air-quality-index/wisconsin-counties?period=2003.
N1  - Publisher attribution: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
ER  -
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Questions

Which county has the highest median Air Quality Index (US EPA)?

Grant County, with 52 in 2003, according to the U.S. Environmental Protection Agency.

Which county has the lowest median Air Quality Index (US EPA)?

Forest County, with 8 in 2003.

Where does this ranking come from?

Every value comes from one source and one period, so the places are comparable: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: median daily AQI. Retrieved 2026-10-12. 13 counties have no value for 2003 and are not ranked.

Median Air Quality Index (US EPA): other rankings

Counties in Wisconsin: more rankings